Japanese unexamined patent application publication No. JP-A-2000-214654 (Hereinafter, Patent document 1) describes a related art image forming apparatus. In the related art image forming apparatus such as an electrophotographic printer, a photosensitive unit having a photosensitive drum and a developing unit having a developing roller are mounted together in a process unit.
In the image forming apparatus of this type, a drive source for generating driving force for rotating the photosensitive drum and the developing roller is provided in an apparatus main body thereof. The process unit includes a drive input member for driving the photosensitive drum and a drive input member for driving the developing roller. In addition, coupling gearwheels are connected, respectively, to the drive input members, so that driving force from the drive source is inputted into the respective drive input members via their mating coupling gearwheels to thereby be transmitted to the photosensitive drum and the developing roller from their mating drive input members.
The respective coupling gearwheels can be connected or engaged with their mating drive input members when the process unit is disposed in a constant position. Because of this, in the event that the process unit is shifted with the respective coupling gearwheels kept engaged with their mating drive input members, the engagement between the respective drive input members and their mating coupling gearwheels is disengaged, the transmission of driving force from the respective coupling gearwheels to their mating drive input members becomes impossible.